This invention relates to a magnetic recording medium which has excellent reliability and in which magnetic recording is performed with high density, a manufacturing method thereof and a magnetic disc device used in an auxiliary storage apparatus of a computer.
A magnetic disc apparatus used in a storage apparatus of a large-scale computer, a work station, a personal computer and the like has been yearly increased in its importance and developed into a mass-stored and small sized device. Increasing of recording density is essential to the development of the magnetic disc apparatus into mass-stored and small-sized apparatus. As the technology for realizing the development into the mass-stored and small-sized device, cited is reduction in distance between a magnetic recording layer of a magnetic recording medium and a magnetic head.
The magnetic recording medium manufactured by sputtering has been provided with a protective layer heretofore for the purpose of protecting a magnetic layer from sliding of a magnetic head. Thinning of the protective layer and reduction of distance between the surface of the protective layer and the magnetic head are the most effective means for more decreasing the distance between a magnetic recording layer and the magnetic head. For this protective layer, carbon manufactured by DC sputtering, RF sputtering (Japanese Patent Laid Open Hei 5-174369), or CVD (Japanese Patent Laid-Open No. Hei 4-90125) is most generally used, and a method of mixing nitrogen atoms, hydrogen atoms and the like in the film to obtain a protective layer more excellent in strength (Japanese Patent Laid-Open No. Sho 62-246129) has been generally adopted.
Various attempts are being made to improve the productivity and slide resistance of a DLC layer. For example, a C:N protective layer is formed on a magnetic layer and a DLC layer is further formed on the protective layer in Japanese Laid-open Patent Application No. Hei 6-84168. In Japanese Laid-open Patent Application No. Hei 11-175960, an attempt is made to add nitrogen in the latter half to the final stages of the formation of a DLC layer. However, the DLC protective layers obtained by these methods cannot achieve satisfactory slide resistance when the thickness of the layer is smaller than 4 nm. When the floating height of a magnetic head is reduced to around 10 nm, contact between the magnetic head and a magnetic recording medium occurs intermittently, whereby floating is not stabilized with the result that writing and reading become impossible.
Further, it is general to use perfluoropolyether liquid lubricant for the purpose of reducing friction between the magnetic head and the magnetic recording medium.
As a general method for thinning, cited is to apply diamond-like carbon (DLC) using ion beam deposition (IBD) or chemical vapor deposition (CVD). for a protective layer. DLC, however, bonding strength of carbon atoms and hydrogen atoms in the thin layer is generally strong and also its network has higher continuity as compared with the carbon protective layer provided by the sputtering. Therefore, the problem is that the bonding strength to perfluoropolyether lubricant applied to the protective layer is weak owing to fewer functional groups.
One of performance indexes of the magnetic recording device using the magnetic recording medium is the data transfer rate. The data transfer rate largely depends on the data access time. The access time is composed of the seek time and the rotation waiting time, and to shorten the rotation waiting time by increasing the rotating speed of a magnetic recording medium leads to the improvement in the data transfer rate.
When the rotating speed of the magnetic recording medium is increased, however, centrifugal force is applied to the liquid lubricant on the DLC protective layer of the magnetic recording medium so that as the result of the problem that the bonding strength is weak, the liquid lubricant is driven away toward the outer peripheral part of the magnetic recording medium until it is shaken off from the magnetic recording medium (hereinafter referred to as spin-off). Consequently, the problem encountered is that the lubricant on the magnetic recording medium is decreased to increase the frictional force between the magnetic recording medium and the magnetic head and cause a crash.
In order to solve the problems, attempts have been made to apply surface treatment to the protective layer so as to increase the bonding strength. Japanese Patent Laid-Open No. Sho 62-150526 and Japanese Patent Laid-Open No. Sho 63-2117 disclose that the surface is subjected to plasma treatment. Japanese Patent Laid-Open No. Hei 4-6624 discloses that the surface is subjected to ultraviolet treatment, water treatment, ozonization or the like. Further, Japanese Patent Laid-Open No. Sho 63-2117, Japanese Patent Laid-Open No. Hei 9-30596, Japanese Patent Laid-Open No. Hei 8-225791, Japanese Patent Laid-Open No. Hei 7-210850 and Japanese Patent Laid-Open No. Hei 5-174354 are similar to the above, and all of these disclose that after the protective layer is formed, the surface thereof is subjected to some treatment. These methods, however, have the problem that it is difficult to uniformly treat the whole surface, one additional process is needed in the work, and besides the adhesion of the lubricant is insufficient.
There is generally employed a method of adding a nitrogen gas in addition to a hydrocarbon gas as a raw material in order to provide functional groups including a nitrogen atom to the protective layer. However, most of the nitrogen atoms absorbed into the DLC protective layer form a triple bond with a carbon atom, so-called nitrile group (—C≡N) and are hardly chemically bonded to a lubricant, thereby making it impossible to increase bonding force with the lubricant.